OK, thanks for the information. I was able to unscrew the top cap with great difficulty and a small hammer and block of wood. Some rust inside but not terrible.

Now looking at it, the small knob with the arrow looks like it should move but is frozen up with some white corrosion, rust and paint. There is a "half moon" shaped thing on the bottom which appears it will only allow it to turn so far in one direction.

Is this accurate? Should I try to free it up or leave it alone. Obviously, I'd like for it to be "functional" but don't want to do something to it that it isn't suppose to do.